UK Home SecretaryTheresa May said Friday that raising the threat level from “substantial” to “severe” means that a terror attack on the UK is “highly likely” in view of the conflicts in Iraq and Syria - although there was no intelligence to suggest an attack was “imminent."

Prime Minister David Cameron said at least 500 people had traveled from the UK "to fight in Syria and potentially Iraq". He said Islamic State (IS) extremists - who are attempting to establish a "caliphate", or Islamic state, in the region - represented a "greater and deeper threat to our security than we have known before." He promised new laws to make it easier to take passports away from people traveling abroad to join the conflict.